From 20beb61baace9d25a8c50e4b552d59a86eb84dad Mon Sep 17 00:00:00 2001
From: Matt Hill <MattDHill@users.noreply.github.com>
Date: Wed, 14 Sep 2022 11:21:00 -0600
Subject: [PATCH] much more efficient (#46)

* much more efficient

* update children too

* better compare
---
 client/lib/json-patch-lib.ts |  8 ++--
 client/lib/patch-db.ts       | 73 +++++++++++++++++++++---------------
 2 files changed, 46 insertions(+), 35 deletions(-)

diff --git a/client/lib/json-patch-lib.ts b/client/lib/json-patch-lib.ts
index 10b0d94..8748b89 100644
--- a/client/lib/json-patch-lib.ts
+++ b/client/lib/json-patch-lib.ts
@@ -43,6 +43,10 @@ export function applyOperation<T>(
   doc.data = recursiveApply(doc.data, jsonPathToKeyArray(path), op, value)
 }
 
+export function jsonPathToKeyArray(path: string): string[] {
+  return path.split('/').slice(1)
+}
+
 function recursiveApply<T extends Record<string, any> | any[]>(
   data: T,
   path: readonly string[],
@@ -105,7 +109,3 @@ function recursiveApplyArray<T extends any[]>(
 function isObject(val: any): val is Record<string, unknown> {
   return typeof val === 'object' && val !== null && !Array.isArray(val)
 }
-
-function jsonPathToKeyArray(path: string): string[] {
-  return path.split('/').slice(1)
-}
diff --git a/client/lib/patch-db.ts b/client/lib/patch-db.ts
index bd05301..dd59c7f 100644
--- a/client/lib/patch-db.ts
+++ b/client/lib/patch-db.ts
@@ -1,10 +1,19 @@
 import { Bootstrapper, DBCache, Dump, Revision, Update } from './types'
 import { BehaviorSubject, Observable, Subscription, withLatestFrom } from 'rxjs'
-import { applyOperation, getValueByPointer } from './json-patch-lib'
+import {
+  applyOperation,
+  getValueByPointer,
+  jsonPathToKeyArray,
+} from './json-patch-lib'
 
 export class PatchDB<T extends { [key: string]: any }> {
   private sub: Subscription | null = null
-  private watchedNodes: { [path: string]: BehaviorSubject<any> } = {}
+  private watchedNodes: {
+    [path: string]: {
+      subject: BehaviorSubject<any>
+      pathArr: string[]
+    }
+  } = {}
 
   readonly cache$ = new BehaviorSubject({ sequence: 0, data: {} as T })
 
@@ -27,7 +36,7 @@ export class PatchDB<T extends { [key: string]: any }> {
   stop() {
     if (!this.sub) return
 
-    Object.values(this.watchedNodes).forEach(node => node.complete())
+    Object.values(this.watchedNodes).forEach(node => node.subject.complete())
     this.watchedNodes = {}
     this.sub.unsubscribe()
     this.sub = null
@@ -109,40 +118,30 @@ export class PatchDB<T extends { [key: string]: any }> {
     >
   >
   watch$(...args: (string | number)[]): Observable<any> {
-    const path = `/${args.join('/')}`
+    const path = args.length ? `/${args.join('/')}` : ''
 
-    return new Observable(subscriber => {
+    if (!this.watchedNodes[path]) {
       const data = this.cache$.value.data
       const value = getValueByPointer(data, path)
-      const source = this.watchedNodes[path] || new BehaviorSubject(value)
-      const subscription = source.subscribe(subscriber)
-
-      this.watchedNodes[path] = source
-      this.updateWatchedNode(path, data)
-
-      return () => {
-        subscription.unsubscribe()
-
-        if (!source.observed) {
-          source.complete()
-          delete this.watchedNodes[path]
-        }
+      this.watchedNodes[path] = {
+        subject: new BehaviorSubject(value),
+        pathArr: jsonPathToKeyArray(path),
       }
-    })
+    }
+
+    return this.watchedNodes[path].subject
   }
 
   proccessUpdates(updates: Update<T>[], cache: DBCache<T>) {
     updates.forEach(update => {
-      if (update.id <= cache.sequence) return
-
       if (this.isRevision(update)) {
-        if (update.id > cache.sequence + 1) {
-          console.error(
-            `Received futuristic revision. Expected ${
-              cache.sequence + 1
-            }, got ${update.id}`,
+        const expected = cache.sequence + 1
+        if (update.id < expected) return
+        if (update.id > expected) {
+          return console.error(
+            // unreachable
+            `Received futuristic revision. Expected ${expected}, got ${update.id}`,
           )
-          return
         }
         this.handleRevision(update, cache)
       } else {
@@ -154,8 +153,12 @@ export class PatchDB<T extends { [key: string]: any }> {
   }
 
   private handleRevision(revision: Revision, cache: DBCache<T>): void {
+    // apply opperations
     revision.patch.forEach(op => {
       applyOperation(cache, op)
+    })
+    // update watched nodes
+    revision.patch.forEach(op => {
       this.updateWatchedNodes(op.path, cache.data)
     })
   }
@@ -165,9 +168,10 @@ export class PatchDB<T extends { [key: string]: any }> {
     this.updateWatchedNodes('', cache.data)
   }
 
-  private updateWatchedNodes(revisionPath: string, data: T) {
-    Object.keys(this.watchedNodes).forEach(path => {
-      if (path.includes(revisionPath) || revisionPath.includes(path)) {
+  private updateWatchedNodes(revisionPath: string, data: T): void {
+    const r = jsonPathToKeyArray(revisionPath)
+    Object.entries(this.watchedNodes).forEach(([path, { pathArr }]) => {
+      if (startsWith(pathArr, r) || startsWith(r, pathArr)) {
         this.updateWatchedNode(path, data)
       }
     })
@@ -175,10 +179,17 @@ export class PatchDB<T extends { [key: string]: any }> {
 
   private updateWatchedNode(path: string, data: T): void {
     const value = getValueByPointer(data, path)
-    this.watchedNodes[path].next(value)
+    this.watchedNodes[path].subject.next(value)
   }
 
   private isRevision(update: Update<T>): update is Revision {
     return 'patch' in update
   }
 }
+
+function startsWith(a: string[], b: string[]) {
+  for (let i = 0; i < b.length; i++) {
+    if (a[i] !== b[i]) return false
+  }
+  return true
+}